Process for production of a magnetic head

ABSTRACT

The improved metal-in-gap magnetic head has a thin ferromagnetic metal film and a gap film superposed on an oxide substrate in that order and an intermediate film made of a nonmagnetic metal or a semiconductor is formed either in the space between the oxide substrate and the ferromagnetic film or between the ferromagnetic film and the gap film or in both spaces and then heat treated to provide such a profile that the element forming the intermediate film is of high concentration at the interface between the ferromagnetic film and the oxide substrate or the gap film whereas said element is of low concentration and distributed in a substantially uniform and continuous manner throughout the interior of the ferromagnetic film. 
     The ferromagnetic film is formed preferably of an Fe--Al--Si (Sendust) alloy, an Fe--M--N alloy or an Fe--M--C alloy (M=Zr, Ta, Nb, Hf, etc.). The intermediate film which contributes corrosion resistance is made preferably of at least one of Cr, Al and Si, with its concentration being preferably from 50 at % to less than 100 at % at the interface between the ferromagnetic film and the oxide substrate or the gap film but from 0.5 at % to 10 at % within the ferromagnetic film. To insure that the element which forms the intermediate film is distributed uniformly and continuously within the ferromagnetic film, the intermediate film is preferably heat treated at 500° to 700° C. for a period of 5 to 120 min.

This is a division of application Ser. No. 08/285,530, filed on Aug. 4,1994, U.S. Pat. No. 5,558,944.

BACKGROUND OF THE INVENTION

This invention relates to a magnetic head in which the area around thegap is formed of a thin ferromagnetic metal film, as well as a processfor producing said magnetic head. More particularly, the inventionrelates to a magnetic head characterized by improved corrosionresistance of the thin ferromagnetic metal film.

With a view to providing improved saturated flux density in levitationand other types of magnetic heads, a structure called the metal-in-gaptype has heretofore been adopted and this structure is characterized bythe attachment of a thin film of a ferromagnetic metal such as Sendustto the gap forming face of a substrate (core) which is formed of amagnetic oxide (e.g., ferrite) or a nonmagnetic oxide. A problem withthis approach is that if a thin ferromagnetic metal film is formed onthe ferrite by a deposition technique such as sputtering, an undesirablymodified layer forms between the oxide in the core and the thinferromagnetic metal film, causing deterioration in characteristics suchas increased magnetic resistance or impaired soft magnetic propertiesand, what is more, the modified layer may occasionally serve as apseudo-gap. Another problem with the thin ferromagnetic metal film isthat it can potentially cause corrosion during cutting, cleaning andother steps of the fabrication process.

With a view to solving these problems of undesirable modification andcorrosion, it has been proposed that a magnetic head of the type shownin FIG. 1A (cross-sectional side view) and FIG. 1B (plan view) in whichone of the opposing surfaces of ferrite or otherwise formed substrates 1and 2 is provided with a thin ferromagnetic metal film 3, with an SiO₂or otherwise formed gap member 4 being inserted between the thinferromagnetic metal film 3 and the substrate 2 and bonded by means ofglass 5 should have a film 6 of nonmagnetic metal such as Cr, Ti or Sithat is provided between the thin ferromagnetic metal film 3 and each ofthe substrates 1 and 2. Alternatively, it has been proposed that amagnetic head of the type shown in FIG. 2A (cross-sectional side view)and FIG. 2B (plan view) in which the thin ferromagnetic metal film 3 isformed on the two opposing surfaces of the substrates 1 and 2 shouldhave a film 6 of nonmagnetic metal such as Cr, Ti or Si that is providednot only between the thin ferromagnetic metal film 3 and each of thesubstrates 1 and 2 but also between the gap member 4 and each thinferromagnetic metal film 3. (See Unexamined Published Japanese PatentApplication (kokai) Sho 61-172203 or Unexamined Published JapanesePatent Application (kokai) Hei 4-241205) The basic idea behind theprovision of the nonmagnetic metal film 6 in those prior art magneticheads is to insure that the nonmagnetic metal element will not diffuseso much into the thin ferromagnetic metal film 3 as to widen thepseudo-gap between the magnetic layers and, hence, glass of alow-melting point of about 350° to 450° C. is employed to preventdiffusion of that element during fusion of the substrates 1 and 2 bymeans of glass 5.

However, these conventional magnetic heads have had the problem that itis not always possible to insure satisfactory corrosion resistance forthe thin ferromagnetic metal film 3.

Stated more specifically, the recent trend in magnetic recording andreproduction to increase the density of recording signals on a magneticrecording/reproducing apparatus has made it necessary that theferromagnetic film for use in the magnetic head be formed of a materialhaving a higher saturation flux density Bs. Ferromagnetic films for usein magnetic heads are generally made of FeAlSi (Sendust alloys) and NiFe(permalloys) which have saturation flux densities (Bs) on the order of 1T. Candidates under review for materials having higher saturation fluxdensities are Fe base microcrystalline films typified by those ofFe--M--N and Fe--M--C (M=Zr, Ta, Nb, Hf, etc.) which have saturationflux densities (Bs) in excess of 1.5 T. However, these materials havethe drawback that they contain more Fe than Sendust alloys andpermalloys and, hence, are poor in corrosion resistance.

In order to improve the corrosion resistance of the thin ferromagneticmetal film 3, it has been proposed that the formation of the nonmagneticmetal film 6 be replaced by the addition of certain elements to saidthin metal film 3. Take, for example, Sendust alloys as ferromagneticmetals; addition elements that are effective include elements of groupIVa (Ti, Zr and Hf), elements of group Va (V, Nb and Ta), elements ofthe platinum group (Ru, Rh, Pd, Os, Ir and Pt), Cr, etc. On the otherhand, Cr, Al, Si, etc., have been found to be effective for the Fe-basemicrocrystalline films.

To add these elements to the thin ferromagnetic metal films, sputteringmay be performed using an alloy or composite target that has apredetermined element already added thereto in a predetermined amount.However, the addition of these elements by sputtering will causesegregation and it is difficult to have them distributed uniformly inthe thin ferromagnetic metal film. As a result, one often fails toassure the desired corrosion resistance and the production yield is low.If, on the other hand, the addition of those elements is increased withcare being taken to prevent segregation while insuring to provide apractical level of corrosion resistance, deterioration incharacteristics occurs in one way or another, as exemplified bysignificant decrease in the saturation flux density Bs of the thinferromagnetic metal film 3 or the failure to provide high permeability.Thus, it has been difficult to provide improved corrosion resistancewhile maintaining satisfactory magnetic characteristics.

A further problem concerns adhesion strength and the ferromagnetic filmhas often separated from the oxide substrate during a machining stepsuch as a cutting operation.

SUMMARY OF THE INVENTION

The present invention has been accomplished under these circumstancesand has as an object providing a magnetic head of such a constructionthat the corrosion resistance of the thin ferromagnetic metal film canbe improved by the addition of small amounts of elements.

This object can be attained by a metal-in-gap magnetic head having athin ferromagnetic metal film and a gap film superposed on an oxidesubstrate in that order, characterized in that an intermediate film madeof a nonmagnetic metal or a semiconductor is formed either in the spacebetween the oxide substrate and the ferromagnetic film or between theferromagnetic film and the gap film or in both spaces and then heattreated to provide such a profile that the element forming theintermediate film is of high concentration at the interface between theferromagnetic film and the oxide substrate or the gap film whereas saidelement is of low concentration and distributed in a substantiallyuniform and continuous manner throughout the interior of theferromagnetic film.

In the practice of the invention, the ferromagnetic film is formedpreferably of an Fe--Al--Si (Sendust alloy) system, an Ni--Fe(permalloy) system, an Fe--M--N system or an Fe--M--C system (M=Zr, Ta,Nb, Hf, etc.), with its thickness being generally in the range fromabout 0.2 to 30 μm.

The intermediate film which contributes corrosion resistance is madepreferably of at least one of Cr, Al and Si, with its thickness rangingfrom 30 to 300 Å; the concentration of either one of Cr, Al or Si ispreferably from 50 at % to less than 100 at % at the interface betweenthe ferromagnetic film and the oxide substrate or the gap film but mayrange from 0.5 to 10 at % within the ferromagnetic film.

To insure that the element which forms the intermediate film isdistributed uniformly and continuously throughout the interior of theferromagnetic film, the intermediate film is preferably heat treated at500° to 700° C. for a period of 5 to 120 min.

By thusly diffusing the intermediate film forming element in the thinferromagnetic metal film, the element, even if it is added in smallamounts that will not impair the magnetic characteristics, can bedistributed uniformly throughout the interior of the ferromagnetic metalfilm without causing segregation, whereby satisfactory corrosionresistance can be achieved.

The magnetic head constructed in accordance with the invention hasanother advantage in that the element which forms the intermediate filmis sufficiently diffused into the ferromagnetic film so that theadhesion strength of the latter is improved over the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional side view showing, in part, a magnetichead;

FIG. 1B is a plan view of the head;

FIG. 2A is a cross-sectional side view showing, in part, anothermagnetic head;

FIG. 2B is a plan view of the head;

FIG. 3 shows SIMS profiles in depth direction for a nonmagnetic metalfilm that was not subjected to any subsequent heat treatment;

FIG. 4 shows SIMS profiles in depth direction for a nonmagnetic metalfilm that was formed in accordance with the invention and which wasthereafter subjected to a heat treatment under vacuum for 30 min at 600°C.;

FIG. 5 shows SIMS profiles in depth direction for a thin ferromagneticmetal film which, after the addition of a nonmagnetic element, wassubjected to a heat treatment under vacuum for 30 min at 600° C.;

FIG. 6 shows schematically the distribution of an element in thenonmagnetic metal film in the magnetic head constructed in accordancewith the invention;

FIG. 7 is a graph showing the relationship between the temperature forheat treatment conducted in the present invention and the concentrationof a nonmagnetic element in the thin ferromagnetic film, with the timeof heat treatment being taken as a parameter; and

FIG. 8 is a graph showing the relationship between the temperature forheat treatment conducted in the present invention and the concentrationof a nonmagnetic element in the nonmagnetic metal film, with the time ofheat treatment being taken as a parameter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Consider two types of magnetic heads, one being shown in FIGS. 1A and1B, in which one of the opposing surfaces of ferrite or otherwise formedsubstrates 1 and 2 is provided with a thin ferromagnetic metal film 3,with an SiO₂ or otherwise formed gap member 4 being inserted between thethin ferromagnetic metal film 3 and the substrate 2 and bonded by meansof glass 5, and the other being shown in FIGS. 2A and 2B, in which thethin ferromagnetic metal film 3 is formed on the two opposing surfacesof the substrates 1 and 2. In the first case, an intermediate layer 6 isformed of Cr, Al, Si or the like and provided between the thinferromagnetic metal film 3 and each of the substrates 1 and 2. In thesecond case, the same intermediate layer is provided not only betweenthe thin ferromagnetic metal film 3 and each of the substrates 1 and 2but also between the gap member 4 and each thin ferromagnetic metal film3.

After forming the thin ferromagnetic metal films 3 and the intermediatelayers 6, heat treatment is conducted at a temperature of 500° to 700°C. for 5 to 120 min either in vacuum (≦10⁴⁻⁴ Pa) or in an inert gasatmosphere (e.g., Ar or N₂), so that the element forming theintermediate layers will diffuse into the thin ferromagnetic metalfilms. The heat treatment may be performed in the absence or presence ofan applied magnetic field and if a magnetic field is to be applied, itmay be static or rotating.

The thin ferromagnetic metal films 3 may be those of FeAlSi (Sendustalloys), NiFe (permalloys) or Fe-base microcrystalline alloys such asFe--M--N and Fe--M--C (M=Zr, Ta, Nb, Hf, etc.) and their thicknessranges typically from 0.2 to 30 μm, desirably from 2 to 3 μm.

The intermediate layers 6 are formed of Cr, Al or Si that havecomparatively large diffusion coefficients and which hence can bedistributed uniformly throughout the ferromagnetic metal films 3. Thethickness of the intermediate layers ranges typically from 30 to 300 Å,desirably from 50 to 100 Å. To compose the intermediate layers, Cr, Aland Si may be used either individually or in admixtures; however, if anyone of Cr, Al and Si is used as a constituent element in the thinferromagnetic metal films 3, such element should be excluded from thelist of elements that can be used to form the intermediate layers. Forinstance, if the thin ferromagnetic metal films 3 are made of FeAlSi(Sendust alloys), Cr is the only element that can be used to form theintermediate layers. The upper and lower intermediate layers need not bemade of the same element.

The thin ferromagnetic metal films 3 and the intermediate layers 6 maybe formed of any deposition technique that is selected from amongsputtering (which may be RF sputtering, DC sputtering, conventionalsputtering or magnetron sputtering), ion-beam sputtering, vacuumevaporation and plating. If sputtering techniques are to be used, thefilms may be formed using an Ar-base gas at pressures in the range fromabout 0.1 to 5 Pa with an input power of 0.1 to 10 W/cm². The substratesmay be water-cooled or heated depending on the metal from which thefilms are to be formed.

A three-layer film consisting of Cr (80 Å)/Fe₈₂ Zr₉ N₉ (2 μm)/Cr (250 Å)in the parenthesized thicknesses was formed on an Mn--Zn polycrystallineferrite substrate by RF magnetron sputtering. The sputtering conditionswere as listed below in Table 1.

                  TABLE 1                                                         ______________________________________                                                    Fe--Zr--N film                                                                             Cr film                                              ______________________________________                                        Target        Fe-14 at % Zr  Cr                                               Input power   2.8 W/cm.sup.2 1.7 W/cm.sup.2                                   Gas pressure  Ar + 10% N.sub.2 0.4 Pa                                                                      Ar 0.67 Pa                                       ______________________________________                                    

Two samples were prepared and one of them was not subjected to anysubsequent treatment whereas the other was subjected to a subsequentheat treatment at 600° C. for 30 min in vacuum (≦10⁻⁴ Pa). The twosamples were thereafter examined by SIMS (secondary ion massspectroscopy) and the respective profiles obtained in thicknessdirection are shown in FIGS. 3 and 4. As is clear from FIG. 3, theuntreated sample was substantially devoid of Cr in the interior of thethin ferromagnetic metal film and the SIMS profile in FIG. 4 shows thatthe heat treatment caused Cr to diffuse uniformly into the thinferromagnetic metal film.

For comparison, Cr was added during the formation of an Fe--Zn--N film.Using a composite target consisting of an Fe--Zr target having a Cr chipattached thereto, sputtering was conducted under the same conditions asdescribed above to have a film of Fe₈₀ Zr₈ Cr₄ N₈ deposited in athickness of 2 μm on an Mn--Fe polycrystalline substrate. Aftersubsequent heat treatment in vacuum at 600° C. for 30 min, an SIMSprofile was taken in thickness direction. The result is shown in FIG. 5,from which one can see that Cr was distributed uniformly across thethickness of the thin ferromagnetic film without any pronounced peak oneither the observe or reverse side of the film.

In the next experiment, Al was used as an element to form theintermediate film. The following three layer arrangements were providedon glass ceramics:

A: Al (100 Å)/Fe₈₂ Zr₉ N₉ (2 μm)/Al (100 Å)

B: Fe₈₀ Zr₈ Al₄ N₈ (2 μm)

C: Fe₈₂ Zr₉ N₉ (2 μm)

The samples were then heat treated at 600° C. for 60 min in vacuum(≦10⁻⁴ Pa). For comparison in terms of corrosion resistance, thosesamples were stored in a hot and humid atmosphere (60° C.×95%) and therelative changes in saturation flux density and any changes thatoccurred after 250 hours in the surface and across the thickness waschecked. The results are shown in Table 2 below.

                  TABLE 2                                                         ______________________________________                                                              Color change                                                                                        Across                            Initial                                                                              50 h    100 h  150 h                                                                              200 h                                                                              250 h Surface                                                                             thickness                         ______________________________________                                        A   1.000  0.990   0.987                                                                              0.985                                                                              0.984                                                                              0.982 "A"   "A"                             B   1.000  0.990   0.870                                                                              0.854                                                                              0.829                                                                              0.813 "B"   "B"                             C   1.000  0.865   0.805                                                                              0.773                                                                              0.754                                                                              0.721 "C"   "C"                             ______________________________________                                         A: no change; B: partial change; C: extensive change                     

As one can see from Table 2, sample B which contained aluminum in thethin ferromagnetic metal film experienced less drop in saturation fluxdensity than Al-free sample C and did not undergo any color change evenwhen it was stored in a hot and humid atmosphere. This demonstrates thesuperiority of sample B in terms of corrosion resistance and theretention of characteristics. Table 2 also shows that sample A which wassubjected to heat treatment after forming an Al film on both sides ofthe thin ferromagnetic metal film was even better than sample B in termsof both protection against the decrease in saturation flux density andresistance to corrosion.

To evaluate the use of Cr as an element to form the intermediate film 6,the following three additional samples D to F were prepared andsubsequently heat treated at 600° C. in vacuum for 60 min. The sampleswere then subjected to a corrosion test as above. The test results areshown in Table 3.

D: Cr (100 Å)/Fe₇₄ Al₉ Si₁₇ (2 μm)/ Cr (100 Å)

E: Fe₇₄ Al₈.5 Si₁₆.5 Cr₁.0 (2 μm)

F: Fe₇₄ Al₉ Si₁₇ (2 μm)

                  TABLE 3                                                         ______________________________________                                                              Color change                                                                                        Across                            Initial                                                                              50 h    100 h  150 h                                                                              200 h                                                                              250 h Surface                                                                             thickness                         ______________________________________                                        D   1.000  0.997   0.995                                                                              0.993                                                                              0.992                                                                              0.988 "A"   "A"                             E   1.000  0.948   0.934                                                                              0.922                                                                              0.915                                                                              0.900 "B"   "A"                             F   1.000  0.913   0.895                                                                              0.889                                                                              0.881                                                                              0.870 "C"   "C"                             ______________________________________                                    

It is clear from Table 3 that as in the case of Al, sample E whichincorporated Cr in the thin ferromagnetic metal film experienced lessdrop in saturation flux density than Cr-free sample E. Sample D whichhad a Cr film formed on both sides of the thin ferromagnetic metal filmwas even better than sample E in terms of protection against lowersaturation flux density and color change.

In the next experiment, Si was used as an element to form theintermediate film. The following three additional samples G to I wereprepared, heat treated and subjected to a corrosion test. The testresults are shown in Table 4.

G: Si (100 Å)/Fe₇₅ Zr₁₀ C₁₂ (2 μm)/ Si (100 Å)

H: Fe₇₅ Zr₁₀ Si₃ C₁₂ (2 μm)

I: Fe₇₈ Zr₁₀ C₁₂ (2 μm)

                  TABLE 4                                                         ______________________________________                                                              Color change                                                                                        Across                            Initial                                                                              50 h    100 h  150 h                                                                              200 h                                                                              250 h Surface                                                                             thickness                         ______________________________________                                        G   1.000  0.992   0.990                                                                              0.987                                                                              0.985                                                                              0.984 "A"   "A"                             H   1.000  0.907   0.851                                                                              0.806                                                                              0.795                                                                              0.780 "B"   "B"                             I   1.000  0.854   0.800                                                                              0.765                                                                              0.731                                                                              0.700 "C"   "C"                             ______________________________________                                    

In the next experiment, Cr and al were used in combination as elementsto form the intermediate film. The following two additional samples Jand K were prepared, heat treated and subjected to a corrosion test. Thetest results are shown in Table 5.

J: Cr (100 Å)/Fe₈₂ Zr₉ N₉ (2 μm)/Al (100 Å)

K: Fe₇₈ Zr₉ Cr₂ Al₂ N₉ (2 μm)

C: Fe₈₂ Zr₉ N₉ (2 μm)

                  TABLE 5                                                         ______________________________________                                                              Color change                                                                                        Across                            Initial                                                                              50 h    100 h  150 h                                                                              200 h                                                                              250 h Surface                                                                             thickness                         ______________________________________                                        J   1.000  0.995   0.992                                                                              0.989                                                                              0.986                                                                              0.985 "A"   "A"                             K   1.000  0.910   0.858                                                                              0.812                                                                              0.793                                                                              0.784 "B"   "B"                             C   1.000  0.865   0.805                                                                              0.773                                                                              0.754                                                                              0.721 "C"   "C"                             ______________________________________                                    

In the next experiment, Al and Si were used in combination as elementsto form the intermediate film. The following two additional samples Land M were prepared, heat treated and subjected to a corrosion test. Thetest results are shown in Table 6.

L: Al (100 Å)/Fe₈₂ Zr₉ N₉ (2 μm)/ Si (100 Å)

M: Fe₇₈ Zr₉ Al₂ Si₂ N₉ (2 μm)

C: Fe₈₂ Zr₉ N₉ (2 μm)

                  TABLE 6                                                         ______________________________________                                                              Color change                                                                                        Across                            Initial                                                                              50 h    100 h  150 h                                                                              200 h                                                                              250 h Surface                                                                             thickness                         ______________________________________                                        L   1.000  0.995   0.994                                                                              0.992                                                                              0.990                                                                              0.989 "A"   "A"                             M   1.000  0.913   0.862                                                                              0.829                                                                              0.818                                                                              0.801 "B"   "B"                             C   1.000  0.865   0.805                                                                              0.773                                                                              0.754                                                                              0.721 "C"   "C"                             ______________________________________                                    

In the next experiment, Cr and Si were used in combination as elementsto form the intermediate film. The following two additional samples wereprepared, heat treated and subjected to a corrosion test. The testresults are shown in Table 7.

N: Cr (100 Å)/Fe₇₈ Zr₁₀ C₁₂ (2 μm)/ Si (100 Å)

O: Fe₇₆ Zr₁₀ Cr₂ Si₂ C₁₂ (2 μm)

I: Fe₇₈ Zr₁₀ C₁₂ (2 μm)

                  TABLE 7                                                         ______________________________________                                                              Color change                                                                                        Across                            Initial                                                                              50 h    100 h  150 h                                                                              200 h                                                                              250 h Surface                                                                             thickness                         ______________________________________                                        N   1.000  0.993   0.990                                                                              0.988                                                                              0.986                                                                              0.984 "A"   "A"                             O   1.000  0.909   0.852                                                                              0.822                                                                              0.800                                                                              0.795 "B"   "B"                             I   1.000  0.854   0.800                                                                              0.765                                                                              0.731                                                                              0.700 "C"   "C"                             ______________________________________                                    

Obviously, the results obtained when the intermediate film was formed ofCr--Al, Al--Si, Si--Cr or Cr--Al--Si alloy were similar to thoseobtained when Cr, Al or Si was used as the sole element to form theintermediate film.

An experiment was also conducted using Cr as an element to form theintermediate film, with the thin ferromagnetic metal film being formedfrom a Sendust alloy in a thickness of 2 μm, and the relationshipbetween the diffusion of Cr and corrosion resistance or magneticcharacteristics was investigated. For comparison, the case of adding Crin alloy form was tested.

Laminated films were prepared on glass ceramics (10 mm×10 mm) inaccordance with the invention under the same conditions as set forth inTable 1, forming the ferromagnetic film of Fe₈₂ Zr₉ N₉ in a thickness of2 μm and the intermediate film of Cr. The concentration of Cr in theferromagnetic film was controlled by adjusting the thickness of the Crfilm and the conditions for the heat treatment performed on thelaminated films. As the comparison, a single-layered FeZrCrN film 2 μmthick was prepared under the same conditions using a composite targetthat was made by attaching Cr chips to an Fe--Zr target. Theconcentration of Cr was controlled by adjusting the number of Cr chipsattached to the target. For comparison of corrosion resistance, thesamples were stored in a hot and humid atmosphere (60° C.×95%) for 250hours and the resulting relative changes in saturation flux density werechecked. The changes in magnetic characteristics with the Crconcentration were also checked by measuring the initial value ofpermeability at 5 MHz before the samples were subjected to the endurancetest. Permeability measurements were conducted by the 8-figure coilmethod in an applied magnetic field of 5 mOe. The results ofmeasurements are shown in Table 8 below.

                  TABLE 8                                                         ______________________________________                                        Concentration                                                                            Invention      Comparison                                          (at %) of Cr in the                                                                      Bs (250 h)/        Bs (250 h)/                                     ferromagnetic film                                                                       Bs (0)    μ 5 MHz                                                                             Bs (0)  μ 5 MHz                              ______________________________________                                        0.1        0.728     3,500    0.728   3.500                                   0.5        0.903     3,600    0.735   3,500                                   1.0        0.938     3,300    0.744   3,300                                   2.5        0.958     3,200    0.772   3,300                                   5.0        0.990     3,200    0.815   3,200                                   7.5        0.995     2,500    0.881   2,600                                   10.0       0.998     2,200    0.890   2,000                                   12.5       0.998     1,500    0.902   1,400                                   15.0       0.998     1,000    0.916     900                                   ______________________________________                                    

As one can see from Table 8, the laminated film samples of the inventionexperienced no more than 10% loss in saturation flux density when the Crconcentration of the ferromagnetic film was at least 0.5 at %; however,to achieve the same result in the comparative samples (Cr added asalloy), the Cr concentration had to be at least 10 at %. The drop insaturation flux density was due to deterioration of the ferromagneticfilm and the smaller the drop, the higher the corrosion resistance ofthe film. On the other hand, the permeability characteristicdeteriorated at Cr concentrations in excess of 10 at %. Hence,satisfactory corrosion resistance is assured if the concentration of Cr(or Al or Si) in the ferromagnetic film is at least 0.5 at % but itsmagnetic characteristics deteriorate if the Cr concentration exceeds 10at %. If Cr is to be added in the form of an alloy as in the comparativesamples, it cannot be incorporated uniformly unless its concentration isat least ten-odd atomic percent; however, if Cr is to be diffused byconducting a heat treatment in accordance with the invention, it can bedistributed uniformly even if its concentration is no more than 10 at %.Based on these observations, one can conclude that in accordance withthe invention, thin ferromagnetic metal films that are satisfactory interms of both corrosion resistance and magnetic characteristics can beformed by adjusting the concentration of Cr (or Al or Si) in theferromagnetic film to lie in the range from 0.5 to 10 at %, preferably1.0 to 10 at %, more preferably 2.5 to 10 at %.

Another experiment was conducted with the nonmagnetic metal film beingformed of Cr. In this experiment, the concentration of a nonmagneticelement Cr at the interface between the substrate and the intermediatefilm was varied to evaluate the peel strength of the intermediate filmfrom the substrate. The substrate was a polycrystalline Mn--Znsubstrate, on which a Cr film and an Fe₈₂ Zr₉ N₉ (2 μm) film weredeposited in superposition. The interfacial Cr concentration wasadjusted by varying the thickness of the Cr film. The samples were thensubjected to a heat treatment that was conducted at 600° C. in vacuo for60 min. A comparative sample was prepared without forming the Crintermediate layer. The results of the peel test conducted on thesamples are shown in Table 9 below.

                  TABLE 9                                                         ______________________________________                                        Interfacial Cr concentration                                                                    Peel strength (in                                           (at %)            relative values)                                            ______________________________________                                        ≧90        2.1                                                         80-90             1.9                                                         70-80             1.8                                                         60-70             1.7                                                         50-60             1.6                                                         <50               1.5                                                         0 (comparison)    1.0                                                         ______________________________________                                    

Peel strength measurements were conducted by a scratch test and theresults were evaluated in terms of relative values, with the value forthe comparative sample taken as unity. When the interfacial Crconcentration was at least 50 at %, the samples exhibited peel strengthvalues at least 1.5 times as high as the value for the comparativesample. To maintain such high Cr levels, the thickness of theintermediate film is adjusted to lie preferably in the range from 30 to200 Å, more preferably from 50 to 100 Å, assuming a thin ferromagneticmetal film 2 to 3 μm thick. The intermediate film having this range ofthickness is also effective in preventing the generation of apseudo-gap.

The heat treatment in accordance with the invention may be performedafter the formation of the gap shown in FIGS. 1A and 2A or it may beconducted while the substrates 1 and 2 are fused together by means ofglass 5. FIG. 6 shows schematically how the element forming theintermediate layer is distributed in the magnetic head produced by theinvention.

FIG. 7 is a graph showing how the concentration of Cr in a thinferromagnetic Sendust film (2 μm thick) changed with the temperature forheat treatment (400°-700° C.) at four varying treatment times in thecase where the intermediate layer was formed of Cr in a thickness of 100Å. FIG. 8 is a similar graph except that it shows the changes of theconcentration of Cr in the nonmagnetic metal film. In order to insurethat the concentrations of Cr in the thin ferromagnetic metal film andin the nonmagnetic film are held within the ranges specified herein andto minimize the period of heat treatment while preventing thedeterioration of magnetic characteristics, the temperature for the heattreatment is adjusted to be preferably within the range from 500° to700° C. whereas the period of the treatment is adjusted to liepreferably within the range from 5 to 120 min.

As described on the foregoing pages, heat treatment is conducted in theinvention in order to insure that the trace elements for providingimproved corrosion resistance are diffused within the thin ferromagneticmetal film and, as a result, those elements are diffused uniformlywithout causing segregation, whereby the corrosion resistance of thefilm can be improved and yet its magnetic characteristics are notimpaired. As a further advantage, the peel strength of the thinferromagnetic metal film adhering to the substrate can be enhancedsatisfactorily.

What is claimed is:
 1. A process comprising the steps of:forming anintermediate film comprising a non-magnetic metal or a semiconductorelement (a) between an oxide substrate and a ferromagnetic film, (b)between a ferromagnetic film and a gap film, or both (a) and (b), toform at least one intermediate film-ferromagnetic film interface;heating said intermediate film at a temperature sufficient to diffusesaid non-magnetic metal or semiconductor element into said ferromagneticfilm forming a concentration of said non-magnetic metal or semiconductorelement at said intermediate film-ferromagnetic film interface which ishigher than the concentration of said non-magnetic metal orsemiconductor element at the interior of said ferromagnetic film and aconcentration of said nonmagnetic metal or semiconductor elementdistributed in a substantially uniform and continuous manner throughoutthe interior of said ferromagnetic film which is lower than theconcentration of said non-magnetic metal or semiconductor element atsaid intermediate film-ferromagnetic film interface.
 2. The process ofclaim 1, wherein said intermediate film is formed both between saidoxide substrate and said ferromagnetic film and between saidferromagnetic film and said gap film.
 3. The process of claim 1, whereinsaid heating is performed at a temperature of 500°-700° C.
 4. Theprocess of claim 3, wherein said heating is performed for a period of5-120 minutes.
 5. The process of claim 1, wherein said intermediate filmcomprises a non-magnetic metal.
 6. The process of claim 5, wherein saidnon-magnetic metal is selected from the group consisting of Cr, Al, Siand alloys thereof.
 7. The process of claim 1, wherein said intermediatefilm comprises a semiconductor element.
 8. The process of claim 1,wherein said intermediate film has a thickness of 30-300 angstroms. 9.The process of claim 1, wherein said ferromagnetic film has a thicknessof 0.2 to 30 microns.
 10. A process, comprising the steps of:forming anintermediate film comprising a non-magnetic metal (a) between an oxidesubstrate and a ferromagnetic film and (b) between said ferromagneticfilm and a gap film to form intermediate film-ferromagnetic filminterfaces; heating said intermediate film at a temperature sufficientto diffuse said non-magnetic metal into said ferromagnetic film whereinsaid heating forms a concentration of said non-magnetic metal of atleast 50 at % but less than 100 at % at said intermediatefilm-ferromagnetic film interfaces and a concentration of saidnon-magnetic metal of from 0.5 at % up to 10 at % at the interior ofsaid ferromagnetic film.
 11. A process, comprising the steps of:formingan intermediate film comprising a non-magnetic metal (a) between anoxide substrate and a ferromagnetic film, (b) between a ferromagneticfilm and a gap film, or both (a) and (b), to form at least oneintermediate film-ferromagnetic film interface; heating saidintermediate film at a temperature sufficient to diffuse saidnon-magnetic metal into said ferromagnetic film, wherein said heatingforms a concentration of said non-magnetic metal of at least 50 at % butless than 100 at % at said intermediate film-ferromagnetic filminterface and a concentration of said non-magnetic metal of from 0.5 at% up to 10 at % at the interior of said ferromagnetic film.